The present invention relates to an apparatus and a method for reproducing data from an optical disk having digital signals recorded thereon.
Known disk data reproducing apparatuses include compact disk (CD) players. Disk type storage media such as CDs generally have their data recorded by what is known as the constant linear velocity (CLV) method to maximize their recording density. The disk type medium with its data recorded by the CLV method differs in revolving speed between the innermost and the outermost tracks: the speed at the outermost track is about 2.6 times that at the innermost track. During data reproduction, the revolving speed of the medium varies with the pickup moving over the medium surface to read data therefrom. During access to a target position on the disk, the revolving speed varies by a factor of up to 2.6. Given such revolving speed fluctuations, data cannot be reproduced from the disk unless and until a predetermined linear velocity is reached.
The technique disclosed by Japanese Patent Laid-Open No. Hei 5-250804 consists in controlling at a constant angular velocity (CAV) the disk whose data was recorded by the CLV method, with a master clock altered in accordance with the pickup position on the disk surface. One disadvantage of the disclosed technique is structural complexity brought on by the need to install revolving speed detecting means whereby the motor is rotated at a constant velocity.
Japanese Patent Laid-Open No. Hei 6-89506 proposes a method whereby the medium is controlled at a constant linear velocity during normal data reproduction and at a constant angular velocity only during access to specific medium positions. The proposed method requires computing the disk revolutions and the clock frequency based on both the current and the accessed pickup positions, with a clock signal generated according to the computed results. This tends to increase the quantity of computations involved, so much so that the computations sometimes continue beyond the period of an access operation.
Another conventional scheme involves performing demodulation and error correction based on a regenerative clock signal in synchronism with the disk revolutions through the use of a PLL circuit. Under this scheme, a clock signal is reproduced in synchronism with the input data so that the clock signal may be used for demodulation and error correction. The scheme is intended to provide smooth demodulation at access time.